Automated warehouses and automated storage and retrieval systems (AS/RS) can reduce costs, pilferage, and damage in storing goods in part because far fewer workers are needed for otherwise similar operations. In typical AS/RS systems, a crane-like apparatus attached to the ceiling and floor of the warehouse is used to transport and position loads. Some systems have developed motorized carts which are used to transport, access, and store pallets of material in multi-story railed structures. For example, in a warehouse, a product on a pallet may be lifted and retracted into a loading elevator shaft by a forklift-like attachment (FLA). The load is transported to a desired level of the railway, removed from the elevator, and placed on a temporary pallet support near the elevator. Next, an aisle cart corresponding to the level where the load was transported moves underneath the load. A lifting row cart is positioned on top of the aisle cart and actuates a lifting mechanism to remove the load from the temporary pallet support. The aisle cart then transports the load and row cart down the aisle to a designated row, where the row cart separates from the aisle cart while carrying the load down a row railway to the final destination of the load. When a load is retrieved from the storage structure, the process is reversed. These actions are typically all automated by a control center at the warehouse.
Typically, a row cart lifts and carries a load on an upper lifting surface as it moves through railways. In one example, the lifting surface is lifted by a central vertically-oriented cylindrical cam via cam followers bolted to the underside of the lifting surface, such as to a support frame under a lid of the lifting surface. When the central cam is rotated, the lid is raised and lowered due to the motion of the cam followers along the cam profile surface. The cart then moves about the railway and lowers the load by again rotating the cam so that the cam followers move to a lower cam profile surface. In some cases, the entire load is centrally supported by a total surface area of approximately twelve square inches. The small size of the support area may lead to instability of the load on the lifting surface at least in part because of the rate by which the cart accelerates and decelerates as it moves through the railway. High acceleration may cause the load to tilt, teeter, twist, and move as it is carried by the row cart, leading to problems such as catching on other structures in the area, becoming imbalanced and disheveled, and thus applying uneven stresses to the central cam and lifting surface. As a result, the central lifting cam cart may generally function disorderly and imprecise.
Row carts are generally small and light, and are designed to lift, move, and lower pallet loads efficiently. Presently-used central cams can throw loads off-balance or cause damage to cam motors when they move the loaded lifting surface from a full down position to a full up position. These undesirable effects can be minimized in part by driving the cams relatively slowly, but this solution also wastes time in the busy warehouse setting. As long as a row cart remains in a row railway, there is less time available for other row carts to use at least that portion of the row railway. The availability of the aisle cart matched with the row cart and other components in the chain of events of the AS/RS system may also be dependent upon the speed with which the row cart can perform its duties.
Some row carts may have multiple cam shafts or drive axles for cams or wheels on the cart. All of these components often must be synchronized in rotation for the cart to operate properly. Typically, a chain and sprocket or a belt running from one of the shafts to another synchronizes the rotation of one shaft with the other. This design is not ideally low-profile, not easy to maintain and assemble, not conservative of its energy source, and not efficient in its use of the space within its enclosure. The mechanical linkages often require the cart to be larger, and require lubrication, repositioning of wandering sprockets, other maintenance, and periodic examination for safety. They also waste power output of the motor (and therefore onboard energy storage) through transmission losses. Furthermore, they take up valuable space inside the limited area available in the cart.
Existing lifting carts are difficult and time-consuming to maintain as well, since access to the internal components typically requires a technician to take time to at least partially disassemble portions of the cart, make the necessary inspections and repairs, and then take time again to reassemble the cart to its original state.